4,037 research outputs found
Mass renormalisation for improved staggered quarks
Improved staggered quark actions are designed to suppress flavour changing
strong interactions. We discuss the perturbation theory for this type of
actions and show the improvements to reduce the quark mass renormalisation
compared to naive staggered quarks. The renormalisations are of similar size as
for Wilson quarks.Comment: LaTeX, 3 pages, Lattice2001(spectrum
The Improvement Program in Nonrelativistic Lattice QCD
Progress in the improvement program in nonrelativistic lattice QCD is
outlined. The leading radiative corrections to the heavy-quark mass
renormalization, energy shift, and two important kinetic coupling coefficients
are presented. The reliability of tadpole-improved perturbation theory in
determining the energy shift and mass renormalization is demonstrated.Comment: 3 pages in uuencoded-compressed-PostScript format, to appear in the
Proceedings of LATTICE 93, Dallas, USA, October 1993; Edinburgh Preprint
93/53
Spectroscopy from Lattice QCD
We present first results for spectroscopy using Lattice
Non-Relativistic QCD (NRQCD). For the NRQCD action the leading order
spin-dependent and next to leading order spin-independent interactions have
been included with tadpole-improved coefficients. We use multi-exponential fits
to multiple correlation functions to extract ground and excited states and
give accurate values for the state hyperfine splitting and the P state
() fine structure, including the effects of mixing.Comment: 12 pages uuencoded latex file + 1 postscript figur
F_B from moving B mesons
We show results for the B meson decay constant calculated both for B mesons
at rest and those with non-zero momentum and using both the temporal and
spatial components of the axial vector current. It is an important check of
lattice systematic errors that all these determinations of f_B should agree. We
also describe how well different smearings for the B meson work at non-zero
momentum - the optimal smearing has a narrow smearing for the b quark.Comment: Lattice2001(heavyquark
Flavor-Symmetry Restoration and Symanzik Improvement for Staggered Quarks
We resolve contradictions in the literature concerning the origins and size
of unphysical flavor-changing strong interactions generated by the
staggered-quark discretization of QCD. We show that the leading contributions
are tree-level in \order(a^2) and that they can be removed by adding three
correction terms to the link operator in the standard action. These corrections
are part of the systematic Symanzik improvement of the staggered-quark action.
We present a new improved action for staggered quarks that is accurate up to
errors of \order(a^4,a^2\alpha_s) --- more accurate than most, if not all,
other discretizations of light-quark dynamics.Comment: 7 page
Semileptonic B Decays from an NRQCD/D234 Action
Semileptonic B decays are studied on quenched anisotropic lattices using
Symanzik improved glue, NRQCD heavy quark and D234 light quark actions. We
employ constrained fits to extract ground state contributions to two- and
three-point correlators. Results for the B --> pi, l nubar decay form factors
are compared with previous lattice results. We find that our systematic errors
(excluding quenching errors) are dominated by chiral extrapolation
uncertainties.Comment: Lattice2002(Heavy quark physics
Finite ma corrections for sea quark matrix elements
We discuss the finite corrections associated with the computation of sea
quark matrix elements. We find them to differ from the standard normalization
used for valence quarks and to depend strongly on the Lorentz structure of the
current under consideration. Phenomenological implications of these results are
briefly discussed in two examples. We also mention how the magnitude of the
correction factors can be reduced by using a 2-link improved action.Comment: 3 pages, contribution to LATTICE'94, uuencoded compressed tar file
(square root removed in equation (1)
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
On the strange quark mass with improved staggered quarks
We present results on the sum of the masses of light and strange quark using
improved staggered quarks. Our calculation uses 2+1 flavours of dynamical
quarks. The effects of the dynamical quarks are clearly visible.Comment: Lattice2002(spectrum) Latex 3 pages, 2 figure
The size of the pion from full lattice QCD with physical u, d, s and c quarks
We present the first calculation of the electromagnetic form factor of the π meson at physical light
quark masses. We use configurations generated by the MILC collaboration including the effect of u, d, s and c sea quarks with the Highly Improved Staggered Quark formalism. We work at three values of the lattice spacing on large volumes and with u/d quark masses going down to the physical value. We study scalar and vector form factors for a range in space-like q2 from 0.0 to -0.13 GeV2 and from their shape we extract mean square radii. Our vector form factor agrees well with experiment and we find hr2iV = 0:403(18)(6) fm2. For the scalar form factor we include quark-line disconnected
contributions which have a significant impact on the radius. We give the first results for SU(3) flavour-singlet and octet scalar mean square radii, obtaining: hr2isinglet
S = 0:506(38)(53)fm2 and hr2ioctet S = 0:431(38)(46)fm2. We discuss the comparison with expectations from chiral perturbation theory
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